1. Field of the Invention
The present invention relates to a resistance change memory having a variable resistive element or a phase-change element as a memory element.
2. Description of the Related Art
Recently, resistance change memories such as ReRAM (Resistive RAM) with a variable resistive element as a memory element and PCRAM (Phase change RAM) with a phase-change element as a memory element are attracting attention as a next-generation nonvolatile semiconductor memory.
Several features of the resistance change memories include (1) a memory cell array of a cross-point type, (2) a large memory capacity realized by three-dimensional integration, and (3) DRAM-like high-speed operation.
When the resistance change memory is put to practical use, for example, the NAND flash memory as a file memory and DRAM as a work memory can be replaced by the resistance change memory.
However, there are many problems to be solved in putting the resistance change memory to practical use. One of the problems is a characteristic and a thickness of a rectifying element necessary for the cross-point type memory cell array.
In the cross-point type memory cell array, the memory element and the rectifying element are connected in series between a word line and a bit line (for example, see Jpn. Pat. Appln. KOKAI Publication Nos. 2005-136425, 2001-236781, 2008-282499, 2007-311772, and 2008-311663).
A large current during application of a forward bias, a small current during application of a reverse bias, and a large breakdown voltage are required for the characteristic of the rectifying element in order to correctly perform the set/reset operation and the read operation.
In order to satisfy the requirements, it is necessary to increase the thickness of the rectifying element. When the thickness of the rectifying element increases, an aspect ratio of a trench formed after the processing of the rectifying element becomes large, which is disadvantageous as regards three-dimensional integration of memory cell arrays.